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// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_NUMERICS_SAFE_CONVERSIONS_H_
#define BASE_NUMERICS_SAFE_CONVERSIONS_H_
#include <stddef.h>
#include <limits>
#include <type_traits>
#include "base/numerics/safe_conversions_impl.h"
#if !defined(__native_client__) && (defined(__ARMEL__) || defined(__arch64__))
#include "base/numerics/safe_conversions_arm_impl.h"
#define BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS (1)
#else
#define BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS (0)
#endif
#if !BASE_NUMERICS_DISABLE_OSTREAM_OPERATORS
#include <ostream>
#endif
namespace base {
namespace internal {
#if !BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS
template <typename Dst, typename Src>
struct SaturateFastAsmOp {
static const bool is_supported = false;
static constexpr Dst Do(Src) {
// Force a compile failure if instantiated.
return CheckOnFailure::template HandleFailure<Dst>();
}
};
#endif // BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS
#undef BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS
// The following special case a few specific integer conversions where we can
// eke out better performance than range checking.
template <typename Dst, typename Src, typename Enable = void>
struct IsValueInRangeFastOp {
static const bool is_supported = false;
static constexpr bool Do(Src value) {
// Force a compile failure if instantiated.
return CheckOnFailure::template HandleFailure<bool>();
}
};
// Signed to signed range comparison.
template <typename Dst, typename Src>
struct IsValueInRangeFastOp<
Dst,
Src,
typename std::enable_if<
std::is_integral<Dst>::value && std::is_integral<Src>::value &&
std::is_signed<Dst>::value && std::is_signed<Src>::value &&
!IsTypeInRangeForNumericType<Dst, Src>::value>::type> {
static const bool is_supported = true;
static constexpr bool Do(Src value) {
// Just downcast to the smaller type, sign extend it back to the original
// type, and then see if it matches the original value.
return value == static_cast<Dst>(value);
}
};
// Signed to unsigned range comparison.
template <typename Dst, typename Src>
struct IsValueInRangeFastOp<
Dst,
Src,
typename std::enable_if<
std::is_integral<Dst>::value && std::is_integral<Src>::value &&
!std::is_signed<Dst>::value && std::is_signed<Src>::value &&
!IsTypeInRangeForNumericType<Dst, Src>::value>::type> {
static const bool is_supported = true;
static constexpr bool Do(Src value) {
// We cast a signed as unsigned to overflow negative values to the top,
// then compare against whichever maximum is smaller, as our upper bound.
return as_unsigned(value) <= as_unsigned(CommonMax<Src, Dst>());
}
};
// Convenience function that returns true if the supplied value is in range
// for the destination type.
template <typename Dst, typename Src>
constexpr bool IsValueInRangeForNumericType(Src value) {
using SrcType = typename internal::UnderlyingType<Src>::type;
return internal::IsValueInRangeFastOp<Dst, SrcType>::is_supported
? internal::IsValueInRangeFastOp<Dst, SrcType>::Do(
static_cast<SrcType>(value))
: internal::DstRangeRelationToSrcRange<Dst>(
static_cast<SrcType>(value))
.IsValid();
}
// checked_cast<> is analogous to static_cast<> for numeric types,
// except that it CHECKs that the specified numeric conversion will not
// overflow or underflow. NaN source will always trigger a CHECK.
template <typename Dst,
class CheckHandler = internal::CheckOnFailure,
typename Src>
constexpr Dst checked_cast(Src value) {
// This throws a compile-time error on evaluating the constexpr if it can be
// determined at compile-time as failing, otherwise it will CHECK at runtime.
using SrcType = typename internal::UnderlyingType<Src>::type;
return BASE_NUMERICS_LIKELY((IsValueInRangeForNumericType<Dst>(value)))
? static_cast<Dst>(static_cast<SrcType>(value))
: CheckHandler::template HandleFailure<Dst>();
}
// Default boundaries for integral/float: max/infinity, lowest/-infinity, 0/NaN.
// You may provide your own limits (e.g. to saturated_cast) so long as you
// implement all of the static constexpr member functions in the class below.
template <typename T>
struct SaturationDefaultLimits : public std::numeric_limits<T> {
static constexpr T NaN() {
return std::numeric_limits<T>::has_quiet_NaN
? std::numeric_limits<T>::quiet_NaN()
: T();
}
using std::numeric_limits<T>::max;
static constexpr T Overflow() {
return std::numeric_limits<T>::has_infinity
? std::numeric_limits<T>::infinity()
: std::numeric_limits<T>::max();
}
using std::numeric_limits<T>::lowest;
static constexpr T Underflow() {
return std::numeric_limits<T>::has_infinity
? std::numeric_limits<T>::infinity() * -1
: std::numeric_limits<T>::lowest();
}
};
template <typename Dst, template <typename> class S, typename Src>
constexpr Dst saturated_cast_impl(Src value, RangeCheck constraint) {
// For some reason clang generates much better code when the branch is
// structured exactly this way, rather than a sequence of checks.
return !constraint.IsOverflowFlagSet()
? (!constraint.IsUnderflowFlagSet() ? static_cast<Dst>(value)
: S<Dst>::Underflow())
// Skip this check for integral Src, which cannot be NaN.
: (std::is_integral<Src>::value || !constraint.IsUnderflowFlagSet()
? S<Dst>::Overflow()
: S<Dst>::NaN());
}
// We can reduce the number of conditions and get slightly better performance
// for normal signed and unsigned integer ranges. And in the specific case of
// Arm, we can use the optimized saturation instructions.
template <typename Dst, typename Src, typename Enable = void>
struct SaturateFastOp {
static const bool is_supported = false;
static constexpr Dst Do(Src value) {
// Force a compile failure if instantiated.
return CheckOnFailure::template HandleFailure<Dst>();
}
};
template <typename Dst, typename Src>
struct SaturateFastOp<
Dst,
Src,
typename std::enable_if<std::is_integral<Src>::value &&
std::is_integral<Dst>::value &&
SaturateFastAsmOp<Dst, Src>::is_supported>::type> {
static const bool is_supported = true;
static Dst Do(Src value) { return SaturateFastAsmOp<Dst, Src>::Do(value); }
};
template <typename Dst, typename Src>
struct SaturateFastOp<
Dst,
Src,
typename std::enable_if<std::is_integral<Src>::value &&
std::is_integral<Dst>::value &&
!SaturateFastAsmOp<Dst, Src>::is_supported>::type> {
static const bool is_supported = true;
static Dst Do(Src value) {
// The exact order of the following is structured to hit the correct
// optimization heuristics across compilers. Do not change without
// checking the emitted code.
Dst saturated = CommonMaxOrMin<Dst, Src>(
IsMaxInRangeForNumericType<Dst, Src>() ||
(!IsMinInRangeForNumericType<Dst, Src>() && IsValueNegative(value)));
return BASE_NUMERICS_LIKELY(IsValueInRangeForNumericType<Dst>(value))
? static_cast<Dst>(value)
: saturated;
}
};
// saturated_cast<> is analogous to static_cast<> for numeric types, except
// that the specified numeric conversion will saturate by default rather than
// overflow or underflow, and NaN assignment to an integral will return 0.
// All boundary condition behaviors can be overriden with a custom handler.
template <typename Dst,
template <typename> class SaturationHandler = SaturationDefaultLimits,
typename Src>
constexpr Dst saturated_cast(Src value) {
using SrcType = typename UnderlyingType<Src>::type;
return !IsCompileTimeConstant(value) &&
SaturateFastOp<Dst, SrcType>::is_supported &&
std::is_same<SaturationHandler<Dst>,
SaturationDefaultLimits<Dst>>::value
? SaturateFastOp<Dst, SrcType>::Do(static_cast<SrcType>(value))
: saturated_cast_impl<Dst, SaturationHandler, SrcType>(
static_cast<SrcType>(value),
DstRangeRelationToSrcRange<Dst, SaturationHandler, SrcType>(
static_cast<SrcType>(value)));
}
// strict_cast<> is analogous to static_cast<> for numeric types, except that
// it will cause a compile failure if the destination type is not large enough
// to contain any value in the source type. It performs no runtime checking.
template <typename Dst, typename Src>
constexpr Dst strict_cast(Src value) {
using SrcType = typename UnderlyingType<Src>::type;
static_assert(UnderlyingType<Src>::is_numeric, "Argument must be numeric.");
static_assert(std::is_arithmetic<Dst>::value, "Result must be numeric.");
// If you got here from a compiler error, it's because you tried to assign
// from a source type to a destination type that has insufficient range.
// The solution may be to change the destination type you're assigning to,
// and use one large enough to represent the source.
// Alternatively, you may be better served with the checked_cast<> or
// saturated_cast<> template functions for your particular use case.
static_assert(StaticDstRangeRelationToSrcRange<Dst, SrcType>::value ==
NUMERIC_RANGE_CONTAINED,
"The source type is out of range for the destination type. "
"Please see strict_cast<> comments for more information.");
return static_cast<Dst>(static_cast<SrcType>(value));
}
// Some wrappers to statically check that a type is in range.
template <typename Dst, typename Src, class Enable = void>
struct IsNumericRangeContained {
static const bool value = false;
};
template <typename Dst, typename Src>
struct IsNumericRangeContained<
Dst,
Src,
typename std::enable_if<ArithmeticOrUnderlyingEnum<Dst>::value &&
ArithmeticOrUnderlyingEnum<Src>::value>::type> {
static const bool value = StaticDstRangeRelationToSrcRange<Dst, Src>::value ==
NUMERIC_RANGE_CONTAINED;
};
// StrictNumeric implements compile time range checking between numeric types by
// wrapping assignment operations in a strict_cast. This class is intended to be
// used for function arguments and return types, to ensure the destination type
// can always contain the source type. This is essentially the same as enforcing
// -Wconversion in gcc and C4302 warnings on MSVC, but it can be applied
// incrementally at API boundaries, making it easier to convert code so that it
// compiles cleanly with truncation warnings enabled.
// This template should introduce no runtime overhead, but it also provides no
// runtime checking of any of the associated mathematical operations. Use
// CheckedNumeric for runtime range checks of the actual value being assigned.
template <typename T>
class StrictNumeric {
public:
using type = T;
constexpr StrictNumeric() : value_(0) {}
// Copy constructor.
template <typename Src>
constexpr StrictNumeric(const StrictNumeric<Src>& rhs)
: value_(strict_cast<T>(rhs.value_)) {}
// This is not an explicit constructor because we implicitly upgrade regular
// numerics to StrictNumerics to make them easier to use.
template <typename Src>
constexpr StrictNumeric(Src value) // NOLINT(runtime/explicit)
: value_(strict_cast<T>(value)) {}
// If you got here from a compiler error, it's because you tried to assign
// from a source type to a destination type that has insufficient range.
// The solution may be to change the destination type you're assigning to,
// and use one large enough to represent the source.
// If you're assigning from a CheckedNumeric<> class, you may be able to use
// the AssignIfValid() member function, specify a narrower destination type to
// the member value functions (e.g. val.template ValueOrDie<Dst>()), use one
// of the value helper functions (e.g. ValueOrDieForType<Dst>(val)).
// If you've encountered an _ambiguous overload_ you can use a static_cast<>
// to explicitly cast the result to the destination type.
// If none of that works, you may be better served with the checked_cast<> or
// saturated_cast<> template functions for your particular use case.
template <typename Dst,
typename std::enable_if<
IsNumericRangeContained<Dst, T>::value>::type* = nullptr>
constexpr operator Dst() const {
return static_cast<typename ArithmeticOrUnderlyingEnum<Dst>::type>(value_);
}
private:
const T value_;
};
// Convience wrapper returns a StrictNumeric from the provided arithmetic type.
template <typename T>
constexpr StrictNumeric<typename UnderlyingType<T>::type> MakeStrictNum(
const T value) {
return value;
}
#if !BASE_NUMERICS_DISABLE_OSTREAM_OPERATORS
// Overload the ostream output operator to make logging work nicely.
template <typename T>
std::ostream& operator<<(std::ostream& os, const StrictNumeric<T>& value) {
os << static_cast<T>(value);
return os;
}
#endif
#define BASE_NUMERIC_COMPARISON_OPERATORS(CLASS, NAME, OP) \
template <typename L, typename R, \
typename std::enable_if< \
internal::Is##CLASS##Op<L, R>::value>::type* = nullptr> \
constexpr bool operator OP(const L lhs, const R rhs) { \
return SafeCompare<NAME, typename UnderlyingType<L>::type, \
typename UnderlyingType<R>::type>(lhs, rhs); \
}
BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsLess, <)
BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsLessOrEqual, <=)
BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsGreater, >)
BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsGreaterOrEqual, >=)
BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsEqual, ==)
BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsNotEqual, !=)
} // namespace internal
using internal::as_signed;
using internal::as_unsigned;
using internal::checked_cast;
using internal::strict_cast;
using internal::saturated_cast;
using internal::SafeUnsignedAbs;
using internal::StrictNumeric;
using internal::MakeStrictNum;
using internal::IsValueInRangeForNumericType;
using internal::IsTypeInRangeForNumericType;
using internal::IsValueNegative;
// Explicitly make a shorter size_t alias for convenience.
using SizeT = StrictNumeric<size_t>;
} // namespace base
#endif // BASE_NUMERICS_SAFE_CONVERSIONS_H_